Re: [Qemu-devel] [PATCH] 9pfs: fix v9fs_lock error case

[Greg Kurz <groug@kaod.org>]

On Thu, 26 Jan 2017 11:07:05 +0100
Paolo Bonzini <pbonzini@redhat.com> wrote:

> In this case, we are marshaling an error status instead of the errno value.
> Reorganize the out and out_nofid labels to look like all the other cases.
> Coverity reports this because the "err = -ENOENT" and "err = -EINVAL"
> assignments above are dead, overwritten by the call to pdu_marshal.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---

There was a confusion indeed: if the server fails it should report it to the
client with an RERROR message.

Responding an RLOCK message with a P9_LOCK_ERROR status only makes sense
when actually implementing locking (i.e. calling flock() on the backend),
which isn't the case in QEMU as stated in the comment above v9fs_lock(). 
We should hence always report a P9_LOCK_SUCCESS status when responding
an RLOCK message.

Just to make it clear, I've modified your patch to open code this and
pushed it to https://github.com/gkurz/qemu/commits/9p-next .

BTW, I've registered to https://scan.coverity.com/projects/qemu as
Peter suggested on IRC. I'll have a look at the other 9pfs issues.

Cheers.

--
Greg

>  hw/9pfs/9p.c | 11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
> index 99e9472..d028eca 100644
> --- a/hw/9pfs/9p.c
> +++ b/hw/9pfs/9p.c
> @@ -3045,14 +3045,15 @@ static void coroutine_fn v9fs_lock(void *opaque)
>          goto out;
>      }
>      status = P9_LOCK_SUCCESS;
> -out:
> -    put_fid(pdu, fidp);
> -out_nofid:
>      err = pdu_marshal(pdu, offset, "b", status);
> -    if (err > 0) {
> -        err += offset;
> +    if (err < 0) {
> +        goto out;
>      }
> +    err += offset;
>      trace_v9fs_lock_return(pdu->tag, pdu->id, status);
> +out:
> +    put_fid(pdu, fidp);
> +out_nofid:
>      pdu_complete(pdu, err);
>      v9fs_string_free(&flock.client_id);
>  }